1. Field of the Invention
The present invention relates generally to a fuel injection system, in which a fuel in a fuel tank is pressurized and supplied to a fuel delivery pipe by a fuel pump and is injected to an induction system of an internal combustion engine, by means of a fuel injection valve provided in the fuel delivery pipe. More specifically, the invention relates to a fuel injection system employing a vane type fuel pump, in which an inner rotor is eccentrically arranged within an internal bore of a housing in rotatable fashion, rollers are kept in contact with the inner periphery of the internal bore of the housing and radially moved in back-and-forth according to rotation of the inner rotor to perform suction and discharge of the fuel in the duel tank, and a pump speed of the fuel pump is controlled depending upon an electric signal from an electric control unit receiving an electric signal from a pressure sensor detecting a fuel pressure in the fuel delivery pipe and electric signals from various sensors detecting an engine operating condition.
2. Description of the Related Art
The vane type fuel pump of the type set forth above is frequently employed in a fuel injection system. As is known in the art, such vane type fuel pump may have higher discharge pressure than a Wesco-type fuel pump. Therefore, the vane type fuel pump is frequently employed in the fuel injection system which injects fuel directly into combustion chambers of the internal combustion engine.
FIG. 3 shows a fuel injection system employing a conventional vane type fuel pump. In FIG. 3, the reference numeral 30 denotes a vane-type fuel pump assembly. The vane-type fuel pump assembly 30 includes a motor portion M which has an output shaft 31, an armature 32 and commutator 33 mounted on the output shaft 31, a brush assembly 34 contacting with the commutator 33, and a pair of permanent magnets 36 arranged within a casing 35 in opposition to the armature 32. Upper and lower portions of the output shaft 31 are rotatably supported by bearing members 37. P denotes a pump portion of the vane-type fuel pump assembly 30, which includes an inner rotor driven to rotate by the output shaft 31 of the motor portion M, rollers driven to move in back-and-forth in radial direction of the inner roller with keeping contact with the inner periphery of the internal bore of the housing, a suction side cover covering one end surface of the housing and formed with a suction port, and a discharge side cover covering the other end surface of the housing and formed with a discharge port (which detailed structure is not shown in the drawings). These motor portion M and the pump portion P are housed within a casing 35. Then, a fuel suction passage 38 communicated with the suction port of the pump portion P opens to the one end of the casing 35, and is connected to the fuel tank 7 storing a fuel. A fuel discharge passage 39 opening to the other end of the casing 35 via the outer circumference of the motor portion M is connected to a fuel delivery pipe D, to which one or more fuel injection valves J are provided.
It should be noted that the reference numeral 40 denotes a check valve arranged within the fuel discharge passage 39, which performs only fuel flow from the fuel discharge passage 39 into the fuel delivery pipe D for blocking surge flow of the fuel. The reference numeral 41 denotes a bypass passage communicating of the portion of the fuel discharge passage 39 located at the upstream side to the check valve 40 to the fuel suction passage 38, bypassing the pump portion P. Within the bypass passage 41, a normally closed pressure relief valve 42 which establish fuel communication through the bypass passage 41 when the fuel pressure within the fuel discharge passage 39 upstream side of the check valve 40 is elevated to be higher than or equal to a given pressure. The reference numeral 43 denotes an electronic control unit (hereinafter referred to as "ECU") receiving an electric signal from a pressure sensor 44 detecting a fuel pressure in the fuel delivery pipe D and electric signals from various sensors 45 detecting the engine operating condition, and outputs an electric control signal to the brush assembly 34 of the motor portion M.
With the construction as set forth above, the motor portion M is driven for revolution by application of the electric control signal from the ECU 43 to the commutator 33 via the brush assembly 34. The revolution of the commutator is then transmitted to the pump portion P via the output shaft 31 of the motor portion M. Thus, the inner rotor of the pump portion P is driven to rotate to cause back-and-forth movement of the rollers housed in radial recesses of the inner rotor to cause variation of the pump chamber to such the fuel stored in the fuel tank T into the pump portion via the fuel suction passage 38 and pressurized to be circulated into the fuel discharge passage 39. On the other hand, the pressurized fuel fed into the fuel discharge passage 39 is supplied into the duel delivery pipe D with opening the check valve 40, and then injected into the induction system or the combustion chamber of the internal combustion engine through the fuel injection valve J.
When the fuel pressure in the fuel delivery pipe D is lower than a predetermined desired fuel pressure, the pressure sensor 44 detects the lower pressure condition to feed an electric signal indicative of the low pressure state to the ECU 43. Then, the ECU 43 is responsive to the low fuel pressure indicative electric signal from the pressure sensor 44 to output the electric control signal for increasing motor speed of the motor portion M to the brush assembly 34 of the motor portion M. By the process set forth above, the pressurized fuel with the elevated pressure is supplied to the fuel delivery pipe D from the pump portion D. Thus, the fuel pressure in the fuel delivery pipe D is elevated to the desired pressure level.
On the other hand, when the fuel pressure in the fuel delivery pipe D is higher than the predetermined desired fuel pressure, the pressure sensor 44 detects the higher pressure condition to output the electric signal indicative of the higher pressure state to the ECU 43. Thus, the ECU 43 issues the electric control signal for decelerating the motor speed of the motor portion M and where by for lowering the discharge pressure in the pump portion P. Thus, the motor speed of the motor portion M is lowered to supply the fuel at the lowered pressure and whereby to lower the fuel pressure within the fuel delivery pipe D to the desired pressure level.
Namely, with the shown arrangement, the fuel pressure in the fuel delivery pipe D is appropriately controlled by controlling the motor speed of the motor portion M on the basis of the electric signal from the pressure sensor 44, and whereby is maintained at the desired fuel pressure level.
It should be noted the pressure relief valve 42 arranged in the bypass passage 41 is desired to relief the excess fuel pressure in the bypass passage 41 to the fuel suction passage 38 when the fuel pressure at the fuel discharge passage 39 at the portion upstream of the check valve 40 above the pressure higher than the given pressure.
With the fuel injection system employing the conventional vane-type fuel pump, in the engine resting condition after driving, the check valve 40 automatically blocks the fuel discharge passage 39, the fuel within the fuel discharge passage 39 downstream of the check valve 40 and the fuel delivery pipe D are maintained in the enclosed fuel delivery circuit.
On the other hand, in such engine resting condition after driving, the environmental temperature of the engine is high. Particularly, the fuel delivery pipe D and the fuel discharge passage 39 are located in the vicinity of the engine to be exposed to the high temperature condition. Therefore, the temperature of the fuel in the fuel delivery pipe D and the fuel discharge passage 39 downstream of the check valve 40 is elevated. As set forth above, since the fuel pressure in the fuel delivery pipe D and the fuel discharge passage 39 is elevated, it is possible to cause leakage of the fuel through the fuel injection valve J to the engine. Therefore, upon restarting of the engine (hot-start condition), an air/fuel mixture becomes excessively rich to degrade performance of re-starting of the engine. On the other hand, a needle valve arranged in the fuel injection valve is depressed onto a valve seat with an excessive depression force by the elevated fuel pressure. Therefore, upon re-starting of the engine, the response characteristics in opening of the needle valve of the fuel injection valve can be degraded. Furthermore, the fuel delivery pipe D and the fuel discharge passage at the portion downstream of the check valve are required substantial withstanding pressure for bearing the elevated fuel pressure. In addition, since the check valve is also subject elevated fuel pressure to receive excessive depression force for seating onto a valve seat to cause degradation of response characteristics in opening the check valve. Also, the check valve is inherently required substantial mechanical strength for bearing such elevated fuel pressure.